I have done a lot of cedar plank grilling using mostly Salmon and Steelhead. I have also done Cod. Good salmon and steelhead on a cedar plank (done properly) are some of the finest foods to be served, anywhere!
I can also recommend, without reservation, meatloaf on a plank.
The "trick" when using a plank on the grill (either gas or charcoal) is to have the plank just under kindling temperature. You WANT the smoke but flame is a no-no).
I nearly always use my Performers and find that one full Weber chimney of lit spread evenly over the grate with all vents open (but lid closed) works perfectly. Cooking time varies from 7.5 minutes to as much as 20 minutes depending on the thickness of the fish. Of course, meatloaf being much thicker takes longer (but using a therm probe in the meatloaf makes it easy).
After the grill is up to heat, I put the food side of the plank down over the coals for two minutes to sterilize the soaked plank. Then, I flip the plank, close the lid and wait until it starts to smoke. Then, I put the fish on, close the lid and grill. The idea is to just grill the fish just until the fish can be "flaked". That way, you will retain maximum moisture for fantastic flavor. Always leave the skin on and do it skin side down. You do NOT need to flip the fish. When it is just right, the fat layer between the skin will melt allowing you to slip a spatula between the skin and the flesh.
Keep on smokin',
Dale53